Internal combustion engine with pressure responsive supercharger bypass

ABSTRACT

This invention provides means for improving the low speed performance of a supercharged internal combustion engine. The means comprises, in combination with an internal combustion engine, a one-way valve in direct fluid flow connection between the fuel/air induction means, e.g. carburetor, and the combustion chamber and a supercharger in parallel fluid flow relationship to the one-way valve. At low engine speed most of the fuel/air mixture passes directly from the, e.g. carburetor, to the combustion chamber, but at higher engine speeds the valve closes and all of the fuel/air mixture is supercharged.

llnited States Patent [191 Keller 1 Mar. 4, r975 [75] Inventor: Robert A. Keller, Smithtown, NY.

[73] Assignee: The Echlin Manufacturing Company, Branford, Conn.

22 Filed: May 17, 1973 211 Appl. No.: 361,203

[52] US. Cl. 60/600, 60/611, 123/119 CE [51] Int. Cl. FOZb 33/44 [58] Field of Search 60/13, 600, 611; 123/119 CE, 119 C [56] References Cited UNITED STATES PATENTS 2.196.247 4/1940 Browne et a1 60/13 2.292.233 8/1942 Lysholm 123/119 C 2.645.409 7/1953 Lawler 60/13 3.143.849 8/1964 Glamann 60/13 3,324,651 6/1967 Smith et a1 60/13 3,380,245 4/1968 Mick 60/13 3.651.636 3/1972 Glassey et a1 60/13 Primary E.\'aminerCarlton R. Croyle Assistant Examiner-Warren Olsen Attorney, Agent, or Firm-Lilling & Siegel [57] ABSTRACT This invention provides means for improving the low speed performance of a supercharged internal c0mbustion engine. The means comprises, in combination with an internal combustion engine, a one-way valve in direct fluid flow connection between the fuel/air induction means, e.g. carburetor, and the combustion chamber and a supercharger in parallel fluid flow relationship to the one-way valve. At low engine speed most of the fuel/air mixture passes directly from the, e.g. carburetor, to the combustion chamber, but at higher engine speeds the valve closes and all of the fuel/air mixture is supercharged.

12 Claims, 6 Drawing Figures INTERNAL COMBUSTION ENGINE WITH PRESSURE RESPONSIVE SUPERCHARGER BYPASS It is well known in the art to pressurize the induction system of an internal combustion engine such that the fuel-air mixture is supplied to the combustion chamber of the engine under advanced pressure. Perhaps the most common method of pressurizing the fuel-air charge to the engine is by the use of a compressor. Such compressor is generally of a centrifugal type which is generally wholly or partially driven by, for example, a turbine powered by the engine exhaust gases; this serves to utilize the energy in the exhaust gases, which would otherwise be completely lost through the exhaust system, to increase the mass of the air/fuel mixture supplied to the engine cylinders by raising the pressure in the engine induction system. A selfregulating mechanism is thus formed wherein the increased speed of operation of the engine generates increased exhaust gases, which in turn generate increased power for operating the compressor, which in turn provides a more efficient fuel/air mixture to the inlet to the combustion chamber; such centrifugal type compressors are shown, for example, in U.S. Pat. Nos. 3,380,245 to Mick, and No. 2,903,847 to Boyd.

Centrifugal type compressors have also been utilized commonly for aircraft engines. The use in such cases, however, generally is directed to increasing the density of the air prior to admixture with the fuel, when the aircraft is operating at higher altitudes, so as to establish a pressure condition at the carburetor intake approaching sea level, or at least of some substantially constant value, regardless of altitude. There is generally no attempt to provide a supercharged, or above sea level pressure, condition, for the purpose of increasing the power of the engine. In other words, the compressor is generally used in aircraft for compensating for the decrease in pressure at higher altitudes so as to allow the engine to operate without constant control or correction of the carburetor. The effect of the use of a compressor on aircraft engines is to provide for a constant horsepower curve regardless of actual engine altitude by providing for the carburetor a substantially constant feed pressure.

The aircraft superchargers are also generally centrifugal compressors driven by a turbine powered by the exhaust gases. Generally, such superchargers have provision in the exhaust system, for bypassing the supercharger turbine when operating at ground level, i.e., at takeoff, where the supercharged air is not needed and where all of the engine power should be used to operate the propellers and not to operate the compressor. See for example, U.S. Pat. No. 2,645,409 to Lawler.

One practical treatise on the applications of the centrifugal supercharger to automobile engines, marine engines and two-stroke cycle engines for motorcycles or so-called snowmobiles", is entitled How to Select and Install Turbochargers, Bill Fisher (Editor), (H. P. Books, Los Altos, Calif. 1971).

The present invention provides means whereby an internal combustion engine, especially for ground level uses, can be supercharged, when needed, but can be operated without supercharging during idle or low speed, low demand operations. During such low speed operations, the flow path of the fuel/air mixture is directly into the internal combustion engine, bypassing the compressor completely; as the demand on, and speed of, the engine is increased, more of the air/fuel mixture flow is directed into the compressor and the supercharging or pressurization of the air/fuel mixture increases with increasing engine speed. The transition from non-supercharge to supercharge operation is gradual and avoids any sudden changes in air/fuel mixture pressure. Furthermore, the air/fuel mixture induction line, upstream of the combustion chamber of the engine, can be kept relatively short so as to eliminate the problems of acceleration lag and rough idle which have been associated with supercharged engines as a result of a carburetor located remotely from the engine combustion chamber.

This invention comprises the combination, with an internal combustion engine, the engine having a combustion chamber, a fluid induction, or fuel/air inlet, conduit to feed a fuel/air mixture to the combustion chamber, and an exhaust conduit to carry exhaust fluid from the combustion chamber, of l) one-way valve means in the induction conduit designed and adapted to permit flow in a direction towards the combustion chamber but to automatically close so as to prevent fluid flow in a direction from the combustion chamber through the inlet conduit, 2) supercharging means in fluid flow connection with the inlet conduit in parallel flow relationship to the one-way valve, and 3) means for driving the supercharging means, the energy for such driving means being provided by the engine wherein an increase in engine speed and engine demand results in an increase in energy provided to the supercharger and thereby an increase in supercharging effect. Preferably, the driving means are in fluid flow connection with the engine exhaust conduit, whereby the exhaust fluid provides the energy for the driving means.

The valve means, most commonly a check valve, is responsive to pressure drop, such that when the pressure downstream of the valve, i.e., towards the combustion chamber, is greater than the pressure upstream of the valve, the valve tends to close. The downstream side of the check valve is exposed to the outlet pressure from the supercharging means; as operation of the supercharging means increases from its idle point, the pressure downstream of the valve increases. When the pressure downstream is greater than the pressure upstream, the check valve closes to prevent reverse flow. Ideally, the check valve acts as a weightless element, and thus closes as soon as the pressure drop reverses to prevent any reverse flow. To compensate for the weight of an actual valve member, bias means can be provided to bias the valve towardsthe closed position, in a known manner.

The supercharging means inlet is in fluid flow connection with the fuel/air inlet conduit upstream of the one-way valve, preferably as close as possible to the valve. The outlet from the compressor supercharger is in fluid flow connection downstream of the one-way valve and preferably as close as possible to the valve. The pressure exerted on the one-way valve by the outlet from the supercharger gradually overcomes the upstream pressure on the conduit as the speed of the supercharger increases so as to cause the valve to close. The effect of the closing of the valve is to divert the fuel/air mixture to the supercharging means where it is compressed before being returned to the conduit downstream of the valve.

In a preferred embodiment, a fuel/air mixing means, such as a carburetor or fuel injector, is provided in fluid flow connection with the fuel/air inlet conduit for inducing a mixture of fuel and air into the inlet conduit. The mixing means is preferably in direct connection with the fuel/air inlet conduit, preferably in a straight line with the valve, such that flow from the mixing means proceeds in a straight line directly into and through the valve (when the valve is open). The inlet to, and outlet from, the supercharging means are preferably connected into the fuel/air inlet conduit immediately upstream and downstream, respectively, of the valve, transversely to the axis of the conduit. Optimally, the angle between the inlet to, and outlet from, the supercharging means and the axis of the fuel/air inlet conduit is 90; thus, the fuel/air mixture passing through the fuel/air inlet conduit tends to flow primarily through the valve and by-pass the supercharging means. Thus, the length of the inlet conduit to the combustion chamber is increased only by the short section required to house the check valve and the supercharger inlet and outlet connections.

The valve means is intended to permit flow only in the direction towards the combustion chamber through the fuel/air inlet conduit. The valve means is preferably, because of simplicity and compactness, a check valve directly responsive to the fluid flow in the conduit, which is opened by the pressure of the fluidflowing in the proper direction. As soon as the flow tends to reverse, i.e. when the pressure on the combustion chamber side of the valve becomes greater than that on the inlet side of the valve, the valve closes. The closing of the valve is ideally done solely by fluid pressure. In actual situations, the check valve is biased toward the closed position, either by, e.g. spring means, or gravity means. The most common types of check valves are the lift check valve, ballcheck valve and swing check valve. Other useful, but generally more complex and bulky, valves include, e.g., the selfoperated pressure regulators. These valves are conventional and well known to the art, and the specific designs thereof are not a part of this invention.

The supercharger preferably comprises a centrifugal compressor driven by a turbine which is in turn driven by exhaust gases from the engine. The turbine is in fluid flow connection with the exhaust conduit from the combustion chamber of the engine. As the speed and demand on the engine increase, the amount of fuel burned increases and thus the amount of exhaust gas generated is increased; the turbine speed thus increases, in turn increasing the speed and output of the centrifugal compressor.

The system provided in accordance with this invention, thus results in a device which avoids the usual problems of low speed operation with a supercharger, i.e., rough idle and lag in acceleration, in the past caused by the distance the fuel/air mixture must travel when the, e.g., carburetor, is in direct fluid connection with the supercharging means. This system permits a low speed operation where the fluid flow distance, between the, for example, carburetor and the combustion chamber, is only very slightly increased over that of a non-supercharged engine. The problem arises primarily at low engine speeds because the fuel/air suspension formed by, e.g., the carburetor, is usually too coarse to maintain itself at the lower velocities over a relatively great distance. Thus, this invention results in the advantages of, e.g., a naturally aspirated carburetor, at low engine speed, plus the undeniable advantages of a supercharged fuel/air mixture at higher engine speeds and demands.

Further, conventional supercharge operation requires heating the fuel/air mixture at the carburetor base, thus heating the fuel/air mixture being fed to the supercharger to prevent fuel fall-out at low engine speeds. This would tend to decrease compressor efficiency and increases detonation tendency of the fuellair mixture during the supercharging high speed operation. It is possible with this invention to heat the fuel- /air mixture downstream of the compressor outlet.

Although centrifugal compressors are preferred, because of their operating simplicity and durability, positive displacement compressors can also be utilized. Such devices would preferably be driven via mechanical connecting means, by the drive shaft in an internal combustion engine, e.g., by the fan belt. The design for the centrifugal compressors and drive turbines and of the positive displacement compressors, as well as the power means connecting the drive turbines or other drive means to the compressor, are well known and conventional in the art. Such designs, therefore, do not form a part of this invention.

The above advantages of the invention will be more fully understood by reference to the following description and drawings of preferred embodiments of the invention selected for purposes of illustration. The preferred embodiments as described below and illustrated in the enclosed drawings, are only exemplary of the scope of this invention and are not intended to be exclusive thereof.

Referring to the drawings:

FIGS. 1 and 1a are schematic, elevation views partly in section, showing a turbo supercharger in parallel fluid flow with the induction conduit, with the valve means in open and closed position, respectively, in accordance with the present invention.

FIGS. 2 and 2a are schematic, elevation views partly in section, of another embodiment of this invention, with a relief valve, showing the valve means in the open and closed positions respectively.

FIGS. 3 and 3a are schematic elevation views, partly in section, of another embodiment with a relief valve, showing the valve means in open and closed positions, respectively.

Referring to FIG. 1, a down draft carburetor 10, or other fuel/air mixing means, e.g., fuel injection means, is connected to an induction, or fuel/air inlet, conduit 12, housing a swing check valve 14 biased by spring means 16 in the hinged joint, and valve seat 17. Supercharger inlet 18 is in fluid flow connection with the induction conduit 12 immediately upstream of valve 14 and places the conduit 12 in fluid flow connection with the inlet to a centrifugal compressor 20. An outlet pipe 22 places in fluid flow connection the outlet from the compressor 20 and the induction conduit 12 downstream of the valve 14, thus placing the valve 14 and compressor 20 in parallel fliud flow relation.

As shown schematically, the compressor 20 is directly driven via mechanical linking means 23 by a gas driven turbine 24. As shown schematically by the arrows 25 and 27, the turbine 24 is powered by the exhaust gases from the exhaust system of the internal combustion engine. The connection to the exhaust system and the exhaust system are not shown. Exhaust gases flowing from the turbine, as shown by arrow 27, can be exhausted to the atmosphere either directly or after passing through mufflers or other devices required on the engine. Induction conduit 12 is directly connected to a manifold pipe 26 which in turn is connected to the manifold leading to the combustion chamber, or chambers, of an internal combustion engine (not shown).

In operation, a fuel/air mixture, or suspension, wherein the air is generally the continuous phase, enters from carburetor into induction conduit 12. Under idling conditions, the major portion of the air/fuel mixture passes through valve 14, which as in FIG. 1 is in theopen position, passing directly to the combustion chamber; as the speed of the internal combustion engine is increased, the amount of the exhaust gases 25 passing through the turbine 24 is increased and the speed of the turbine increases; this, in turn, directly increases the speed of the centrifugal compressor 20, increasing the proportion of fuel/air mixture drawn into compressor through inlet 18 and increasing the amount and the pressure of the fuel/air mixture exhausting from outlet conduit 22 into the induction conduit 12. When the pressure downstream of valve 14 is greater than the pressure upstream of valve 14, the check valve 14 closes against valve seat 17. This position is shown in FIG. la. At this time all of the fuel/air mixture passes through the supercharger 20. As the engine speed increases, the exhaust gas flow increases and the degree of supercharging increases.

Thus, this invention provides a means whereby at idle, when valve 14 is open, the supercharging means 20 is substantially out of the circuit and there is only a minimal increase in the length of the conduit between the fuel/air mixing means, the carburetor 10, and the manifold 26. Furthermore, by placing the compressor means 20 on a parallel flow line, not directly beneath the carburetor 10, the heat generated by the compressor does not affect the operation of the carburetor either at low idling speed or, more significantly, at the higher speeds at which heat is generated and at which the greatest effect would be had upon the efficiency of the carburetor and compressor.

The embodiment shown in FIGS. 2 and 2a differs from that of FIG. 1 including a relief valve 30 shown in closed position during the idle stage in FIG. 2 and in open position at advanced higher speeds in FIG. 2a. The relief valve in this embodiment is shown to be a simple spring-loaded disk valve, wherein the valve 32 is held against valve seat 33 by the force exerted by spring 34. Other conventional types of pressure relief valves can be utilized. In order to avoid loss of the fuellair mixture from the relief valve 30 to the atmosphere, (a result which would not only be uneconomical in loss of fuel, but would also create an environment and safety hazard), the valve housing 30 is connected via recycle conduit 36 and an expansion chamber, not shown, to the carburetor inlet; the fuel/air mixture recycled through the conduit 36 is mixed with the fresh fuel and air in the carburetor. The expansion chamber, not shown, is placed in the recycle conduit 36 so as to reduce the pressure, in the fuel/air mixture fed to the carburetor, to atmospheric. This is preferred as it avoids the problems of handling pressurized gases in a carburetor.

The embodiment of FIGS. 2 and 2a, results in a richer fuel/air ratio being delivered to the engine at high engine load and speed. This is desirable in helping to prevent predetonation, in addition to permitting limiting the desired pressure boost of the mixture fed to the combustion chamber.

In operation, the embodiment of FIG. 2, at low engine speeds, operates in the same manner as in FIG. 11, Le, as the engine speed increases to a certain point, the supercharging effect increases until the pressure downstream of valve 14 is greater than that upstream and the swing valve 14 closes. From this time on, the pressure below valve 14 increases until a desired maximum pressure is achieved, at which time the relief valve 32 is opened to limit pressure to the desired value. The fuel- /air fluid mixture escaping through valve 32 is directed via conduit 36 back into the carburetor intake to achieve the richer fuel/air mixture desired.

The embodiment shown in FIGS. 3 and 3a is similar to FIG. 2 in including a pressure relief valve 32; however, in this case, the fluid air/fuel mixture relieved, or throttled, through valve 32, is directed via conduit 40 to the induction conduit, downstream of the carburetor and immediately upstream of valve 14. This results in a somewhat more compact design than that of the embodiment of FIG. 2, and permits maintaining a constant fuel/air ratio in the mixture fed to the engine. At the same time, it permits a control over the pressure boost obtained by the compressor while substantially limiting the amount of power required to attain the desired compressor boost. Maintaining a constant fuel/air ratio can be significant under the recently enacted Environmental Protection Act rules governing vehicles operated by internal combustion engines.

The pressure relief valve means shown in FIGS. 2, 2a, 3 and 3a, are the spring operated disk valve type. How ever, other conventional relief valve designs can be utilized and the specific design of the: relief valve does not constitute a part of the present invention.

In the embodiments shown in the drawings, element 10 is designated as a carburetor, in the exemplified case, a downdraft carburetor including a throttle valve, not shown. It controls the amount of fuel/air mixture fed to the inlet conduit 12, and into the engine, and thus regulates the speed of the engine and the speed of the turbo-compressor. As an alternative to the carburetor shown, a side-draft carburetor can be utilized wherein induction conduit 12 is disposed horizontally rather than vertically in relation to the carburetor. A further alternative includes the use of injection means for forming the fuel/air suspension mixture.

As shown in the drawings, the crux of this invention is the short length of the induction conduit 12 connecting the carburetor 10, or other induction means, to the intake manifold 26 to the internal combustion engine. The conduit 12 thus provides a short path for the normally aspirated fuel/air mixture from the induction means 10 to the intake manifold 26 during nonsupercharged normal operation. The conduit 12 has a flange connection 50 at a first end, connected to the carburetor 10, and a second flange connection 52 at the second end, connected to the intake manifold 26. The inlet conduit 18 and the outlet conduit 22 to the compressor 20 are connected to the side wall of the conduit 12, immediately upstream and downstream,

respectively, of the valve 14. The length of this conduit 12 can be as short as about 1 inch but preferably at least about 1 inch and optimally not greater than about 3 inches. The internal diameters of the inlet conduit 18 to, and the outlet conduit 22 from, the supercharging means can be as little as one-half inch and preferably from about 1 inch to about 3 inches.

The supercharging device of this invention is applicable to any initial combustion invention, but has special application to engines used in vehicles. Such vehicles include not only ground transportation such as automobiles, motorcycles and snowmobiles, but also powered boats and even ground effect vehicles.

The devices of the present invention not only is useful to improve the low-speed performance of a supercharged engine, but also decrease the amount of pollutants expelled by the engine at low speeds. The present invention can be incorporated into an engine including other anti-pollutant, performance-increasing devices. One such recently developed device, which is especially amenable to use in a supercharged engine, is the use of an ultrasonic fuel system in place of a carburetor. Such a system is described in Ultrasonic Fuel System, by J. P. Norby, Popular Science, Vol. 202, No. 3, pages 89-91 (March, 1973).

I claim:

1. In combination with an internal combustion engine, the engine comprising a combustion chamber, induction means for forming a fluid fuel/air mixture, an induction conduit in fluid flow connection with the induction means and the combustion chamber, and means to exhaust fluid from the combustion chamber: 1) a first bypass conduit in fluid flow connection to a first upstream portion of the induction conduit; 2) a supercharging means having an inlet and an outlet, the inlet being in fluid flow connection to the first bypass conduit; 3) drive means for the supercharging means, designed and adapted to directly and continuously utilize the energy provided by the internal combustion engine to power the supercharging means whereby the outlet pressure of the supercharger increases directly as engine power output increases; 4) a second bypass conduit in fluid flow connection with a downstream portion of the induction conduit and with the outlet from the supercharging means, whereby the supercharging means is in parallel fluid flow connection with an intermediate portion of the induction conduit between the first bypass conduit and the second bypass conduit; and 5) valve means in the intermediate portion of the induction conduit, the valve means comprising a valve seat rigidly connected to the interior of the induction conduit and a valve member moveably connected to the interior of the induction conduit and having a first pressure surface exposed to the inlet pressure of the supercharging means upstream of the valve means and a second pressure surface exposed to the pressure of the outlet from the supercharging means downstream of the valve means whereby at low outlet pressures the valve member is located out of contact with the valve seat and at high outlet pressures the valve member is urged toward and placed in contact with the valve seat so as to prevent direct flow through the induction conduit and to cause the passage of all fluid flow around the valve and through the supercharging means via the bypass conduits.

2. The combination of claim I, wherein the supercharging means is a centrifugal compressor.

3. The combination of claim 2, wherein the drive means is designed and adapted to utilize energy in the exhaust fluid from the combustion chamber to drive the centrifugal compressor.

4. The combination of claim 3, wherein the fuel/air mixture fluid flows in a straight line from the induction means through the valve means.

5. The combination of claim 4, comprising an inlet conduit from the induction conduit to the supercharging means and an outlet conduit from the supercharging means to the induction conduit, the inlet conduit being connected transversely to the induction conduit intermediate the induction means and the valve means, and the outlet conduit being connected to the induction conduit at a point intermediate of the valve means and the combustion chamber.

6. The combination of claim 5, wherein the inlet conduit to the supercharging means is connected at an angle of at least about to the direction of flow from the induction means through the induction conduit.

7. The combination of claim 1, wherein the valve means is a check valve.

8. The combination of claim 7, wherein the valve means is biased in the closed position.

9. The combination of claim 1, wherein the supercharging means comprises a centrifugal compressor directly driven by a gas turbine, the gas turbine being in fluid flow connection with the exhaust means of the combustion chamber whereby the exhaust gases from the internal combustion engine drive the gas turbine.

10. The combination of claim 14, comprising in addition, a pressure relief valve in fluid flow connection with the induction conduit, intermediate the valve means and the combustion chamber, whereby pressure build-up caused by the supercharging means can be limited.

11. The combination of claim 10, comprising by-pass conduit means in fluid flow connection with the induction conduit, via the pressure relief valve, and with the inlet to the fuel/air induction means.

12. The combination of claim 10, comprising a bypass conduit in fluid flow connection with the induction conduit via the pressure relief valve and also in fluid flow connection with the induction conduit at a point intermediate the induction means and the valve means. 

1. In combination with an internal combustion engine, the engine comprising a combustion chamber, induction means for forming a fluid fuel/air mixture, an induction conduit in fluid flow connection with the induction means and the combustion chamber, and means to exhaust fluid from the combustion chamber: 1) a first bypass conduit in fluid flow connection to a first upstream portion of the induction conduit; 2) a supercharging means having an inlet and an outlet, the inlet being in fluid flow connection to the first bypass conduit; 3) drive means for the supercharging means, designed and adapted to directly and continuously utilize the energy provided by the internal combustion engine to power the supercharging means whereby the outlet pressure of the supercharger increases directly as engine power output increases; 4) a second bypass conduit in fluid flow connection with a downstream portion of the induction conduit and with the outlet from the supercharging means, whereby the supercharging means is in parallel fluid flow connection with an intermediate portion of the induction conduit between the first bypass conduit and the second bypass conduit; and 5) valve means in the intermediate portion of the induction conduit, the valve means comprising a valve seat rigidly connected to the interior of the induction conduit and a valve member moveably connected to the interior of the induction conduit and having a first pressure surface exposed to the inlet pressure of the supercharging means upstream of the valve means and a second pressure surface exposed to the pressure of the outlet from the supercharging means downstream of the valve means whereby at low outlet pressures the valve member is located out of contact with the valve seat and at high outlet pressures the valve member is urged toward and placed in contact with the valve seat so as to prevent direct flow through the induction conduit and to cause the passage of all fluid flow around the valve and through the supercharging means via the bypass conduits.
 2. The combination of claim 1, wherein the supercharging means is a centrifugal compressor.
 3. The combination of claim 2, wherein the drive means is designed and adapted to utilize energy in the exhaust fluid from the combustion chamber to drive the centrifugal compressor.
 4. The combination of claim 3, wherein the fuel/air mixture fluid flows in a straight line from the induction means through the valve means.
 5. The combination of claim 4, comprising an inlet conduit from the induction conduit to the supercharging means and an outlet conduit from the supercharging means to the induction conduit, the inlet conduit being connected transversely to the induction conduit intermediate the induction means and the valve means, and the outlet conduit being connected to the induction conduit at a point intermediate of the valve means and the combustion chamber.
 6. The combination of claim 5, wherein the inlet conduit to the supercharging means is connected at an angle of at least about 90* to the direction of flow from the induction means through the induction conduit.
 7. The combination of claim 1, wherein the valve means is a check valve.
 8. The combination of claim 7, wherein the valve means is biased in the closed position.
 9. The combination of claim 1, wherein the supercharging means comprises a centrifugal compressor directly driven by a gas turbine, the gas turbine being in fluid flow connection with the exhaust means of the combustion chamber whereby the exhaust gases from the internal combustion engine drive the gas turbine.
 10. The combination of claim 14, comprising in addition, a pressure relief valve in fluid flow connection with the induction conduit, intermediate the valve means and the combustion chamber, whereby pressure build-up caused by the supercharging means can be limited.
 11. The combination of claim 10, comprising by-pass conduit means in fluid flow connection with the induction conduit, via the pressure relief valve, and with the inlet to the fuel/air induction means.
 12. The combination of claim 10, comprising a by-pass conduit in fluid flow connection with the induction conduit via the pressure relief valve and also in fluid flow connection with the induction conduit at a point intermediate the induction means and the valve means. 